Phosphine plasma activation of α-Fe2O3 for high energy asymmetric supercapacitors

We report a phosphine (PH3) plasma activation strategy for significantly boosting the electrochemical performance of supercapacitor electrodes. Using Fe2O3 as a demonstration, we show that the plasma activation simultaneously improves the conductivity, creates atomic-scale vacancies (defects), as well as increases active surface area, and thus leading to a greatly enhanced performance with a high areal capacitance of 340 mF cm(-2) at 1 mA cm(-2), compared to 66 mF cm(-2) of pristine Fe2O3. Moreover, the asymmetric supercapacitor devices based on plasma-activated Fe2O3 anodes and electrodeposited MnO2 cathodes can achieve a high stack energy density of 0.42mWh cm(-3) at a stack power density of 10.3mWcm(-3) along with good stability (88% capacitance retention after 9000 cycles at 10 mA cm(-2)). Our work provides a simple yet effective strategy to greatly enhance the electrochemical performance of Fe2O3 anodes and to further promote their application in asymmetric supercapacitors.